1. Field of the Invention
The present invention relates to the field of eyeglasses and eyeglass frames and methods of manufacture thereof.
2. Prior Art
Cellulose acetate is an attractive material for the manufacture of eyeglass frames, largely because it is easy to work and offers remarkable cosmetic appeal. Accordingly the prior art will be discussed in this context, even though the use of the present invention is not so limited, but instead is also applicable to eyeglass frames fabricated from other plastics.
Cellulose acetate has two primary deficiencies, namely: i) it has a tendency to shrink somewhat over time, and ii) it has poor resistance to mechanical creep. The invention described herein is a technique to overcome the latter, particularly as it affects what is referred to herein as ‘face form’. In particular, a typical pair of eyeglasses is configured with the temples conforming to the wearer's head, but sized so that, when worn, the temples elastically deflect to help keep the eyeglasses in position. However this creates a bending stress on the bridge of the eyeglasses, which for cellulose acetate, overtime will result in permanent deformation and, hence, a loss of the desired ‘face form’.